1. Field of the Invention
This invention relates generally to monitoring the medical condition of a living subject, and more particularly to novel methods and apparatus for noninvasive monitoring of blood-glucose concentration.
The invention is particularly intended for human subjects, but veterinary applications are also within the scope of my invention.
2. Prior Art
Effective diagnosis and treatment of various medical conditions requires a continuing sequence of information about the concentration of glucose in the blood. For example, patients with diabetes mellitus should tailor their diets and insulin dosage, if needed, to their blood-sugar levels.
For many such purposes average or mean values are preferable to instantaneous values, since the latter may reflect very brief fluctuations that are not significant or that could be misleading if used as a basis for treatment.
Ideally, average or mean glucose-concentration measurements should be available on short notice, at low cost, and as frequently as once or twice a day.
Present methods of monitoring the concentration of glucose in the blood of a living subject, however, require withdrawing a sample of blood and analyzing the sample chemically. The process of taking and analyzing a blood sample is not simple, is moderately expensive, is rarely done continually, and provides only instantaneous values.
There is another area of prior art that is relevant to my invention, although it has not heretofore been given a practical use in connection with blood-glucose measurement. It is well known to ophthalmologists that the eye is slowly responsive to the level of glucose in the blood. Abnormally increasing blood glucose causes the focus of the eye to shift toward the patient.
For example, if an old person, with no control over the accommodation (i.e., focus) of her or his eyes, happens to have far vision focused at infinity when that person's blood sugar is normal, the focus will shift to perhaps three feet--causing blurring of distant objects--with increasing abnormal blood sugar.
Because this effect is slow it is not responsive to short-term changes, but integrates blood-sugar content over a time period of about a day.
Yet another relevant area of prior art that has not heretofore been connected with blood-glucose measurement is the general field of optometry. Highly refined methods and apparatus are available for measurement and analysis of vision as such--but, as is well known, the purpose of optometry is to obtain information for correction of vision itself, rather than information for diagnosis or treatment of any other condition.